Q3 will be "extremely difficult" in Melbourne - Sainz

The Italian outfit appears to be firmly within F1 2017's midfield battle on the evidence of testing, with Sainz ending up third-fastest on the final day of pre-season running on Friday.

But the Spaniard, who made it to Q3 nine times last year despite Toro Rosso having used a year-old Ferrari power unit, believes getting into the final segment in Melbourne will be a tough ask.

"I honestly think that the others have done also massive steps - Force India, Haas, Renault in particular, compared to last year," Sainz said. "Williams is flying.

"So it is going to be a very very tight fight for P5 in the championship, or to be the fifth-fastest car in Melbourne - so to get into Q3 will be extremely difficult."

Asked whether he believed Williams was a clear fourth in the pecking order, Sainz said: "I don't know, it's probably a bit too early to know. But they are definitely very strong and they will be very difficult to beat."

Toro Rosso now "in condition to fight"

The STR12 had a difficult start to pre-season testing, as it was last on mileage and laptime after the opening week in Barcelona.

Reliability dramas didn't abate fully during week two, but the team managed to significantly ramp up performance.

Sainz's teammate Daniil Kvyat, whose final pre-season testing day was Thursday, said it was the first day that he could call "good fun" - and admitted the team had been at risk of not being ready for the season-opening Australian Grand Prix.

"We did quite a few race simulation laps, a bit more of performance runs - we've done this work, which to be honest we should have been doing much earlier," Kvyat said on Thursday.

"But at least we managed to do this job, because if we did not have this before Melbourne, than I would say we're not ready.

"But as we managed to do this day, I would say that we are in condition to fight."

Sainz expressed a similar sentiment after closing out the team's test programme on Friday: "Thanks to this last day [of testing] I think the team can be a bit more optimistic and more positive.

"We still have a a lot less laps than our rivals and there's much more potential to unlock from the car. We'll make up for that during the season."

Additional reporting by Oleg Karpov